1. Field of the Invention
The invention disclosed in this specification relates to an object, a method, a method for producing an object, a process, a machine, manufacture, or a composition of matter. In particular, the present invention relates to, for example, a semiconductor device, a display device, a light-emitting device, a driving method thereof, or a manufacturing method thereof. In particular, the present invention relates to, for example, an oxide semiconductor film included in a semiconductor device and a film formation method thereof.
Note that a semiconductor device in this specification and the like refers to all types of devices which can function by utilizing semiconductor characteristics, and electro-optical devices, semiconductor circuits, and electronic devices are all semiconductor devices.
2. Description of the Related Art
A technique by which transistors are formed using semiconductor thin films formed over a substrate having an insulating surface has been attracting attention. Such a transistor is applied to a wide range of electronic devices such as an integrated circuit (IC) and an image display device (also simply referred to as a display device). A silicon-based semiconductor material is widely known as a material for a semiconductor thin film applicable to a transistor. As another material, an oxide semiconductor has been attracting attention.
For example, Patent Document 1 discloses a transistor including an amorphous oxide semiconductor film containing In, Ga, and Zn and having an electron carrier concentration of lower than 1018/cm3, in which a sputtering method is considered the most suitable as a film formation method of the amorphous oxide semiconductor film.
Although a transistor including an oxide semiconductor film can obtain transistor characteristics relatively with ease, the oxide semiconductor film is likely to be amorphous and has unstable physical properties. Thus, it is difficult to secure reliability of such a transistor.
On the other hand, there is a report that a transistor including a crystalline oxide semiconductor film has more excellent electrical characteristics and higher reliability than a transistor including an amorphous oxide semiconductor film (see Non-Patent Document 1).